The use of power electronic devices such as a set of inverters to control a motor drive or other electrically powered device is well known. Components of one prior art motor control system are shown in FIG. 1. FIG. 1 illustrates various embodiments of a power supply (such as an AC motor drive) having nine such power cells. The power cells in FIG. 1 are represented by a block having input terminals A, B, and C; and output terminals T1 and T2. In FIG. 1, a transformer or other multi-winding device 110 receives three-phase, medium-voltage power at its primary winding 112, and delivers power to a load 130 such as a three-phase AC motor via an array of single-phase inverters (also referred to as power cells) 151-153, 161-163, and 171-173. Each phase of the power supply output is fed by a group of series-connected power cells, called herein a “phase-group” 150, 160 and 170.
The transformer 110 includes primary windings 112 that excite a number of secondary windings 114-122. Although primary windings 112 are illustrated as having a star configuration, a mesh configuration is also possible. Further, although secondary windings 114-122 are illustrated as having a delta or an extended-delta configuration, other configurations of windings may be used as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety. In the example of FIG. 1 there is a separate secondary winding for each power cell. However, the number of power cells and/or secondary windings illustrated in FIG. 1 is merely illustrative, and other numbers are possible. Additional details about such a power supply are disclosed in U.S. Pat. No. 5,625,545.
Several functional components of inverters can be subject to high thermal stress during operation. When high temperatures occur, such as a result of temporary overload operation or other operation outside of base ratings, inner temperatures of the components can reach or exceed critical temperatures. Such systems may be cooled by circulating cool water and/or air through the components in order to absorb heat and reduce the component temperature. Nonetheless, it is desirable to sense the temperature of the component to identify when the component approaches a critical temperature.
The large number of temperature measuring locations in a power electronic circuit, and the high thermal stress conditions of operation, make it difficult to adequately sense the temperature of a power electronic device.
This document describes methods and systems that attempt to solve at least some of the problems described above, and/or other problems.